| Abstract [eng] |
In this study, a fully integrated Gas Electron Multiplier (GEM) detector system was employed for high-resolution X-ray imaging. The detector is based on a triple-GEM foil configuration, each with an active area of 10×10cm², housed within a sealed gas chamber. The GEM foils are fabricated from copper foil, featuring a dense array of microscopic holes that enable avalanche multiplication of electrons under high voltage. The triple-GEM cascade ensures high gain, low ion feedback, and excellent spatial resolution. The detector includes a Kapton window, a drift cathode that establishes a uniform electric field across the drift region, guiding primary ionization electrons toward the GEM stack. The multiplied electrons are collected on a 2D readout plate with 256 channels (128 in X and 128 in Y), enabling precise spatial localization of the incident radiation. The readout system is a custom-designed 256-channel board developed by Techtra, interfacing with the GEM detector via four Panasonic® connectors. It integrates four Texas Instruments® DDC264 analog-to-digital converters (ADCs), each offering 64 channels with 20-bit resolution and current-input capability. The detector operates with an Ar/CO₂ (70/30) gas mixture and is powered by a high-voltage supply unit (Caen DT5470N USB HV PS), capable of delivering up to −5kV at 200μA. High-voltage is supplied to the GEM foils via a dedicated HV connector and cable. Gas flow is regulated using a Micromite 1656M4YA dosing valve with micrometric control. The system is housed with dedicated connectors for inputs and outputs, ensuring stable and low-noise operation. To demonstrate the imaging capabilities of the GEM detector, a COOL-X miniature X-ray generator was used. Random objects were placed on the Kapton entrance window and irradiated with X-rays. The COOL-X uses a pyroelectric crystal to generate electrons, which then produce X-rays upon striking a copper target, with peak output reaching approximately 10⁸ photons per second and endpoint energies up to 35kV. |
